For the production of solid materials based on hydraulically setting coating agents such as for example concrete or mortar, mechanical methods and also manual methods are common. However, the properties of the solid materials depend considerably on the nature and manner of their production.
In the manual method, the hydraulically setting coating agents are for example applied onto the substrate with a trowel. In mechanical methods, the hydraulically setting coating agents are supplied in a feed line of a spray nozzle with which the hydraulically setting coating agents are applied onto the substrate in question. Mechanical methods such as for example the dry or wet spray methods are described in DIN 18551. In the dry spray method, hydraulically setting coating agents are used in the form of dry mixtures and made up with water in the spray nozzle. In the wet spray method, aqueous hydraulically setting coating agents are used. In the wet spray method, as in the dry spray method, further additives such as for example setting accelerators can be added to the hydraulically setting coating agents in the spray nozzle. After setting of the hydraulically setting coating agents, the solid materials are obtained.
The strength of the solid materials depends for example on the air content or the density of the solid materials and correlates with the statistical distribution of the air pore diameters (air pore distribution). When the spray method is used, the strength of the solid materials can be increased by forcing the aqueous coating agents through the spray nozzle with compressed air, so that the hydraulically setting coating agents are accelerated to high speeds and finally on impact against the substrate undergo a strong rebound. As a result of the rebound, some of the air escapes from the hydraulically setting coating agents and the hydraulically setting coating agents are compacted. In addition, the air pore distribution in the hydraulically setting coating agent also changes. Overall, the impact leads to an increase in the strength of the hydraulically setting coating agents. The acceleration of hydraulically setting coating agents with compressed air can be quantified using the air consumption factor:Air consumption factor=(compressed air volume/t)/(concrete volume/t)
In the formula for the air consumption factor, the variable t stands for a time value. The air consumption factor is a dimensionless quantity and with mechanical methods normally assumes values of 144 to 240.
The hydraulically setting coating agents applied with compressed air and said air consumption factors result in solid materials which have an air content lower by ca. 5% and hence a correspondingly higher density compared to solid materials produced by the manual method. In addition, the use of compressed air has a very strong influence on the air pore distribution in the hydraulically setting coating agents and in the corresponding solid materials. Thus in solid materials which were made by the manual method usually over 40% of the air pores have a diameter in the range from 500 to 50000 nm. In contrast, in solid materials which were made by the spray method with the aforesaid air consumption factors, usually considerably fewer than 35% of the air pores have a diameter of 500 to 50000 nm.
However, the use of compressed air with the aforesaid air consumption factors in the spray method also has the effect that as a result of the impact against the substrate the hydraulically setting coating agents fall off the substrate again (rebound) to a considerable extent and must be removed from the building side and disposed of as useless waste. The rebound usually amounts to more than 20 percent of the coating. A further disadvantage is the high equipment and energy cost which is associated with the use of compressed air for such high air consumption factors.
The manual method does offer the advantage that hardly any rebound occurs and the equipment costs are low. However, as already discussed above, compared to the mechanical method with the use of compressed air with the aforesaid air consumption factors the manual method has the disadvantage that, owing to the low impact, only solid materials which have a lower density, a higher air content, a different air pore distribution and hence lower strength are obtainable with the manual method.